This invention relates to locating the position of a spot of light and, more particularly, to techniques for determining the X-Y location of a focused laser beam.
In a variety of applications of practical importance, it is necessary to be able to determine the location of a focused light beam. In one such important application, it is necessary to locate the X-Y position of the waist of a focused laser beam formed by a zone plate member. Such members are utilized, for example, on masks and/or wafers for alignment purposes during manufacture of semiconductor devices, as described in detail in U.S. Pat. Nos. 4,037,969, 4,326,805 and 4,398,824.
Various instrumentalities are known for use in a zone plate alignment system to ascertain beam location. One such standard instrumentality comprises a television camera and an associated microprocessor. But efforts by workers in the art have continued to be directed at trying to devise even better ways of carrying out the location function. It was realized that such efforts, if successful, has the potential for improving the alignment capabilities of a zone plate system, and thereby also for improving the quality and reducing the costs of semiconductor devices made utilizing such a system.